Heat oven to 375 degrees F.
Stir together flour, cocoa powder and baking soda in a bowl.
Beat together butter, sugar, vanilla and salt in medium-size bowl until blended, about 1 minute. Add egg; beat 1 minute.
Dissolve espresso powder in very hot water in small cup; stir into butter mixture. Stir in flour mixture. Stir in nuts and white chocolate.
Using 2 rounded tablespoons dough per cookie, place dough balls 2 inches apart on baking sheets.
Bake in 375 degree oven for about 12 minutes or until edges are golden and centers are set. Cool on baking sheets on wire rack 2 minutes. Transfer cookies to rack to cool. Serve warm or room temperature. Makes about 15 cookies.